High fuel efficient automobiles have been developed in order to protect the global environment. For such development, tires for automobiles with high fuel efficiency have also been desired.
Fuel efficiency can generally be improved by reducing rolling resistance. Rolling resistance is largely attributable to energy loss caused by the repeated deformation of the tire during running. In order to reduce rolling resistance, it is suggested that, for example, a tread, which more largely contributes to rolling resistance than any other tire component, be formed to have a two-layer structure in which a rubber composition with small energy loss is provided on the inner side (base layer) and a rubber composition excellent in abrasion resistance is provided on the outer side (cap layer) (see, for example, Patent Literature 1). However, in recent years, fuel efficiency needs to be further improved.
If the amount of filler is reduced in order to further improve fuel efficiency, then the stiffness of a tread tends to be reduced and handling stability tends to be deteriorated. Meanwhile, if crosslink density is increased so as to enhance the stiffness, then abrasion resistance and chipping resistance tend to be deteriorated and the resulting tire tends not to secure sufficient durability. Therefore, a method of improving fuel efficiency while maintaining good handling stability and durability is needed.